Backlight unit and display device including the same

ABSTRACT

A backlight unit includes a light guide plate that includes a side surface that is an incidence surface that is normal to a first direction, a light source adjacent to the incidence surface, and a light conversion layer disposed on an upper surface of the light guide plate that changes a wavelength of light incident thereto. The light conversion layer includes a first portion and a second portion arranged in the first direction. The first portion is closer to the incidence surface in the first direction than the second portion, and the first portion is thinner than the second portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35U.S.C. § 119 from, and the benefit of, Korean Patent Application No.10-2018-0000840, filed on Jan. 3, 2018 in the Korean IntellectualProperty Office, the contents of which are herein incorporated byreference in their entirety.

BACKGROUND

Embodiments of the present disclosure are directed to a display device,and in particular, to a display device with improved display quality.

A next-generation advanced display device with low power consumption,good portability, and high added-value properties has recently come intothe spotlight. Such a display device includes a plurality of pixels, andeach pixel includes a thin-film transistor that controls a switchingoperation or a voltage to be supplied to each pixel.

A display device includes a display panel and a backlight unit thatprovides light to the display panel. The backlight unit includes a lightsource and a light guide plate. Light generated by the light source isincident into the light guide plate and is then provided to the displaypanel.

SUMMARY

Some embodiments of the inventive concept provide a display device withimproved display quality.

According to some embodiments of the inventive concept, a backlight unitincludes a light guide plate that includes a side surface that is anincidence surface that is normal to a first direction, a light sourceadjacent to the incidence surface, and a light conversion layer disposedon an upper surface of the light guide plate that changes a wavelengthof light incident thereto. The light conversion layer includes a firstportion and a second portion arranged in the first direction. The firstportion is closer to the incidence surface in the first direction thanthe second portion, and the first portion is thinner than the secondportion.

In some embodiments, the second portion has a uniform thickness.

In some embodiments, the first portion has a uniform thickness.

In some embodiments, when measured in the first direction, a length ofthe first portion is less than about 5% of a length of the light guideplate.

In some embodiments, the first portion is connected to the secondportion.

In some embodiments, a top surface of the first portion includes aninclined surface in which a thickness of the first portion increases ina direction from the incidence surface toward the second portion.

In some embodiments, the light conversion layer includes a plurality ofquantum dots.

According to some embodiments of the inventive concept, a backlight unitincludes a light guide plate that includes a side surface that is anincidence surface that is normal to a first direction; a light sourceadjacent to the incidence surface that generates a first light towardthe incidence surface; and a light conversion layer disposed on an uppersurface of the light guide plate that changes a wavelength of lightincident thereto. The light conversion layer includes a plurality offirst quantum dots that convert the first light into a second light thathas a different wavelength range from that of the first light and aplurality of second quantum dots that convert the first light into athird light that has a different wavelength range from those of thefirst and second lights.

In some embodiments, the first light is a blue light.

In some embodiments, the light conversion layer includes a first portionand a second portion arranged in the first direction. A number ofquantum dots per unit volume in the first portion is less than that inthe second portion.

In some embodiments, the number of quantum dot per unit volume in thefirst portion increases in a direction from the incidence surface towardthe second portion.

In some embodiments, the first portion is closer to the incidencesurface in the first direction than the second portion, and the firstportion is thinner than the second portion.

In some embodiments, the first portion includes a plurality of patternsthat are spaced apart from each other in the first direction when viewedin a plan view. A distance between adjacent patterns of the plurality ofpatterns decreases in a direction from the incidence surface toward thesecond portion.

In some embodiments, the backlight unit further includes a lowrefraction layer interposed between the light guide plate and the lightconversion layer. A refractive index of the low refraction layer is lessthan those of the light guide plate and the light conversion layer.

In some embodiments, the backlight unit further includes a scatteringmember disposed on the second portion that includes a plurality ofscattering objects. The scattering member does not overlap the firstportion, when viewed in a plan view.

According to some embodiments of the inventive concept, a backlight unitincludes a light guide plate that includes a side surface that is anincidence surface, and a light conversion layer disposed on the lightguide plate, the light conversion layer including a plurality of quantumdots that convert a first light into light that has a differentwavelength range from that of the first light. The light conversionlayer includes a first region and a second region arranged in adirection. The first region is closer to the incidence surface than thesecond region, and a thickness of the light conversion layer in thefirst region is less than that in the second region.

In some embodiments, the backlight unit further includes a light sourceadjacent to the incidence surface that emits the first light toward theincidence surface. The plurality of quantum dots include a plurality offirst quantum dots that convert the first light to a second light havinga different wavelength range from that of the first light; and aplurality of second quantum dots that convert the first light to a thirdlight having a different wavelength range from those of the first andsecond lights.

In some embodiments, an area of a top surface of the first region isless than about one-twentieth of a total area of a top surface of thelight guide plate.

In some embodiments, the light conversion layer in the second region hasa uniform thickness.

In some embodiments, a thickness of the light conversion layer in thefirst region increases in a direction from the incidence surface towardthe second region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a display device according tosome embodiments of the inventive concept.

FIG. 2 is a sectional view taken along line I-I′ of FIG. 1.

FIG. 3 is a sectional view of a backlight unit according to someembodiments of the inventive concept.

FIG. 4 is a top plan view of a backlight unit according to someembodiments of the inventive concept.

FIG. 5 is an enlarged sectional view of a portion ‘A’ of FIG. 2.

FIG. 6 is a sectional view of a backlight unit according to otherembodiments of the inventive concept.

FIG. 7 illustrates propagation paths of light emitted from a lightsource according to other embodiments of the inventive concept.

FIG. 8 is a sectional view of a backlight unit according to otherembodiments of the inventive concept.

FIG. 9 is a top plan view of a backlight unit according to otherembodiments of the inventive concept.

FIG. 10 is a sectional view of a backlight unit according to otherembodiments of the inventive concept.

FIG. 11 is a sectional view of a backlight unit according to otherembodiments of the inventive concept.

It should be noted that these drawings are not to scale and may notprecisely reflect the precise structural or performance characteristicsof any given embodiment. The use of similar or identical referencenumbers in the various drawings may indicate the presence of a similaror identical element or feature.

DETAILED DESCRIPTION

Exemplary embodiments of the inventive concepts will now be describedmore fully with reference to the accompanying drawings, in which exampleembodiments are shown. Exemplary embodiments of the inventive conceptsmay, however, be embodied in many different forms and should not beconstrued as being limited to the embodiments set forth herein. In thedrawings, the thicknesses of layers and regions may be exaggerated forclarity. Like reference numerals in the drawings may denote likeelements, and thus their description will be omitted.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent.

FIG. 1 is an exploded perspective view of a display device according tosome embodiments of the inventive concept, and FIG. 2 is a sectionalview taken along line I-I of FIG. 1.

Referring to FIGS. 1 and 2, a display device 1000 according to someembodiments of the inventive concept has a rectangular shape whose shortsides are parallel to a first direction DR1 and whose long sides areparallel to a second direction DR2. However, embodiments of theinventive concept are not limited to a specific shape of the displaydevice 1000, and the display device 1000 may have various other shapes.

According to some embodiments the display device 1000 includes a windowmember 100, a display panel DM, a backlight unit BLU, and a storagemember 700.

For convenience in description, a propagation direction of image orlight in the display device 1000 will be referred to as an upwarddirection, and a direction opposite to the upward direction will bereferred to as a downward direction. In a present embodiment, the upwardand downward directions are defined to be parallel to a third directionDR3 that is orthogonal to the first and second directions DR1 and DR2.Hereinafter, front and rear surfaces of each of elements to be describedbelow will be differentiated based on the third direction DR3. However,the upward and downward directions are a relative concept, and incertain embodiments, they may be used to indicate other directions.

According to some embodiments, the window structure 100 includes alight-transmitting region TA that allows image light emitted from thedisplay panel DM to pass therethrough, and a light-blocking region CAadjacent to the light-transmitting region TA that prevents image lightfrom passing therethrough. When viewed in a plane defined by the firstand second directions DR1 and DR2, the light-transmitting region TA ispositioned at a center region of the display device 1000. Thelight-blocking region CA is provided at a peripheral region of thelight-transmitting region TA and surrounds the light-transmitting regionTA. For example, the light-blocking region CA has a frame shape.

According to some embodiments, the window member 100 is formed of orincludes at least one of glass, sapphire, or plastic.

According to some embodiments, the display panel DM is disposed belowthe window member 100. The display panel DM displays an image usinglight emitted from the backlight unit BLU. In other words, the displaypanel DM is a light-receiving type display panel. For example, in someembodiments, the display panel DM is a liquid crystal display panel.

According to some embodiments, a surface of the display panel DM thatdisplays an image will be referred to as a display surface. The displaysurface includes a display region DA which is used to display an image,and a non-display region NDA in which no image is displayed. When viewedin a plan view, the display region DA is a center region of the displaypanel DM and overlaps the light-transmitting region TA of the windowmember 100.

According to some embodiments, the backlight unit BLU is disposed belowthe display panel DM and is used to provide light to the display panelDM. In a present embodiment, the backlight unit BLU is an edge-typebacklight unit.

According to some embodiments, the backlight unit BLU includes a lightsource LS, a light guide plate 200, a light conversion layer 300, areflection sheet 400, an optical member 500, and a mold frame 600.

According to some embodiments, the light source LS is disposed adjacentin the first direction DR1 to at least one side surface of the lightguide plate 200. However, embodiments of the inventive concept are notlimited to a specific position of the light source LS, and, for example,the light source LS can be provided adjacent to at least one other sidesurface of the light guide plate 200. The side surface of the lightguide plate 200 adjacent to the light source LS may be referred to as afirst surface S1 (e.g., see FIGS. 3 and 4).

According to some embodiments, light source LS includes a plurality oflight source units LSU and a light source substrate LSS.

According to some embodiments, the light source units LSU can generatelight which is provided to the display panel DM through the light guideplate 200.

In a present embodiment, the light source units LSU generate a firstlight. For example, the first light has a wavelength that ranges fromabout 400 nm to about 500 nm. In other words, the light source units LSUgenerate substantially blue light.

In a present embodiment, each of the light source units LSU is apoint-like light source, such as a light emitting diode (LED). However,embodiments of the inventive concept are not limited to a specific kindof light source unit LSU.

Furthermore, embodiments of the inventive concept are not limited to thenumber of the light source units LSU. In some embodiments, the lightsource unit LSU is a single LED serving as a point-like light source ora plurality of LED groups. In other embodiments, the light source unitsLSU are a linear light source.

According to some embodiments, the light source units LSU is mounted onthe light source substrate LSS. The light source substrate LSS faces aside surface of the light guide plate 200 in the first direction DR1 andextends in the second direction DR2. The light source substrate LSSincludes a light source control unit that is connected to the lightsource units LSU. The light source control unit analyzes an image to bedisplayed on the display panel DM to output a local dimming signal basedon the image analysis, and to control the brightness of light generatedby the light source units LSU based on the local dimming signal. In someembodiments, the light source control unit is mounted on an additionalcircuit substrate, but embodiments of the inventive concept are notlimited to a specific position of the light source control unit.

According to some embodiments, the light guide plate 200 has a plateshape. The light guide plate 200 redirects light received from the lightsource LS toward the display panel DM or in the upward direction.

According to some embodiments, the light guide plate 200 is formed of orincludes a material having a high transmittance to visible light. Forexample, the light guide plate 200 is formed of or includes glass. Insome embodiments, the light guide plate 200 is formed of or includes atransparent polymer resin, such as polymethyl methacrylate (PMMA).

According to some embodiments, the light guide plate 200 has a firstrefractive index. For example, the first refractive index ranges fromabout 1.4 to about 1.55.

According to some embodiments, the light conversion layer 300 isdisposed on the light guide plate 200. In some embodiments, the lightconversion layer 300 is formed on the top surface of the light guideplate 200 by a coating process. The light conversion layer 300 changes awavelength of an incident light. The light conversion layer 300 has asecond refractive index. For example, the second refractive index isequal to or greater than about 1.65. The light conversion layer 300 willbe described in more detail with reference to FIGS. 3 to 5.

According to some embodiments, the reflection sheet 400 is disposedbelow the light guide plate 200. The reflection sheet 400 reflects lightthat has propagated toward a bottom surface of the light guide plate 200in the upward direction. The reflection sheet 400 includes alight-reflective material. For example, the reflection sheet 400 isformed of or includes aluminum or silver.

According to some embodiments, the optical member 500 is disposedbetween the light conversion layer 300 and the display panel DM. Theoptical member 500 diffuses and condenses light received from the lightconversion layer 300 and emits the light toward the display panel DM.

According to some embodiments, the optical member 500 includes aplurality of sheets. For example, the optical member 500 includes adiffusion sheet, a prism sheet, and a protection sheet. The diffusionsheet diffuses light received from the light conversion layer 300. Theprism sheet is disposed on the diffusion sheet and condenses lightdiffused by the diffusion sheet and then emits the light in the upwarddirection.

According to some embodiments, the protection sheet protects prisms ofthe prism sheet against friction caused by external objects. However,embodiments of the inventive concept are not limited to the number ortypes of sheets in the optical member 500.

According to some embodiments, the mold frame 600 is disposed betweenthe light guide plate 200 and the optical member 500. In a presentembodiment, the mold frame 600 has a frame shape. For example, the moldframe 600 is disposed along an edge region of the top surface of thelight guide plate 200. The display panel DM and the optical member 500are placed on the mold frame 600. The mold frame 600 fixes and holds thedisplay panel DM, the optical member 500, and the backlight unit BLU.

According to some embodiments, the storage member 700 is disposed at alowermost level of the display device 1000 and contains the backlightunit BLU. The storage member 700 includes a bottom portion 710 and aplurality of sidewall portions 720 that are connected to the bottomportion 710. In some embodiments, the light source LS is disposed on aninner side surface of one of the sidewall portions 720 of the storagemember 700. The storage member 700 is formed of or includes asufficiently hard metal.

FIG. 3 is a sectional view of a backlight unit according to someembodiments of the inventive concept, and FIG. 4 is a top plan view of abacklight unit according to some embodiments of the inventive concept.For convenience in illustration, those elements of a backlight unitother than a light guide plate and a light conversion layer are omittedfrom FIG. 3.

Referring to FIGS. 3 and 4, according to some embodiments, the lightconversion layer 300 includes a plurality of conversion particles. Eachof the conversion particles absorbs at least a portion of the incidentlight and then emits light with a different color from that of theincident light, or transmits the portion of incident light without achange in color.

According to some embodiments, when the energy of light incident intothe light conversion layer 300 is high enough to excite a conversionparticle, the conversion particle absorbs at least a portion of theincident light, thereby transitioning into an excited state, and thenwhen it decays back to a stable or low-energy state, light whose colordiffers from that of the incident light is emitted from the conversionparticle. By contrast, when the energy of the incident light is too lowto excite the conversion particle, the incident light passes through thelight conversion layer 300 without a change in color.

According to some embodiments, the color of light emitted from theconversion particle is determined by a particle size of the conversionparticle. In general, the larger the particle size, the longer thewavelength of the emitted light, and the smaller the particle size, theshorter the wavelength of the emitted light.

In a present embodiment, each of the conversion particles is a quantumdot (QD). Light emitted from the conversion particles of the lightconversion layer 300 are radiated in various directions.

For example, according to some embodiments, the conversion particlesinclude first quantum dots QD1 and second quantum dots QD2. Each of thefirst quantum dots QD1 converts the first light into a second light byabsorbing the first light and then emitting the second light. Forexample, the second light has a wavelength that ranges from about 640 nmto about 780 nm. In other words, each of the first quantum dots QD1coverts a substantially blue light to red light.

According to some embodiments, each of the second quantum dots QD2converts the first light to a third light by absorbing the first lightand then emitting the third light. For example, the third light has awavelength that ranges from about 480 nm to about 560 nm. In otherwords, each of the second quantum dots QD2 converts a substantially bluelight to green light.

As described above, according to some embodiments, the wavelength of theconverted light is determined by a particle size of the conversionparticles. In a present embodiment, each of the first quantum dots QD1has a particle size larger than that of each of the second quantum dotsQD2.

According to some embodiments, the light conversion layer 300 mayfurther include scattering objects. The scattering objects are mixedwith the first and second quantum dots QD1 and QD2 in the lightconversion layer 300.

In a present embodiment, the light conversion layer 300 includes a firstregion W1 and a second region W2. The first region W1 and the secondregion W2 are arranged in the first direction DR1. The first region W1and the second region W2 are connected to each other. The first regionW1 may be closer to the first surface S1 that is an incidence surface ofthe light guide plate 200 than the second region W2. In other words, thesecond region W2 is closer to a second, opposite surface S2 of the lightguide plate 200 than the first region W1. The first surface S1 and thesecond surface S2 are opposite to each other in the first direction DR1.

In a present embodiment, the light conversion layer 300 includes a firstportion 310 and a second portion 320. The first portion 310 correspondsto the first region W1, and the second portion 320 corresponds to thesecond region W2. In a present embodiment, the first portion 310 and thesecond portion 320 are connected to each other, thereby forming a singlecontinuous object.

According to some embodiments, when measured in the first direction DR1,the first portion 310 has a first length and the second portion 320 hasa second length. In some embodiments, the first length is shorter thanabout 5% of a total length WD of the light guide plate 200 in the firstdirection DR1. In other words, an area of the first region W1 is lessthan about one-twentieth of the total area of the light guide plate 200.

In some embodiments, the first portion 310 is thinner than the secondportion 320. Each of the first portion 310 and the second portion 320has a uniform thickness. The second portion 320 has a thickness of about10 um. This will be described in more detail with reference to FIG. 5.

FIG. 5 is an enlarged sectional view of a portion ‘A’ of FIG. 2. FIG. 5illustrates a propagation path of light emitted from the light sourceLS.

Referring to FIG. 5 in conjunction with FIGS. 3 and 4, according to someembodiments, light emitted by the light source units LSU propagatestoward the light guide plate 200.

According to some embodiments, light that is incident to the light guideplate 200 is incident onto the top surface of the light guide plate 200at an incidence angle that is greater than a critical angle whenmeasured from a direction normal to the top surface of the light guideplate 200. In this case, total reflection of the incident light occursat the top surface of the light guide plate 200. By contrast, when anincidence angle of the incident light is less than the critical angle,the incident light propagates through the light guide plate 200. The topsurface of the light guide plate 200 is a light-emitting surface and,hereinafter is referred to as a third surface S3.

In detail, according to some embodiments, as shown in FIG. 5, lightemitted from the light source LS that is incident to the light guideplate 200 includes a first upward incident light LA1 that is incidentonto the third surface S3 of the light guide plate 200 at a first angleθA relative to a direction normal to the third surface S3. The firstangle θA is greater than the critical angle. Thus, the first upwardincident light LA1 is reflected by the third surface S3 back into thelight guide plate 200, thereby forming first downward reflected lightLA1′.

According to some embodiments, light emitted from the light source LSthat is incident to the light guide plate 200 also includes a firstdownward incident light LA2 that is incident into a fourth surface S4 ofthe light guide plate 200 at the first angle θA relative to a directionnormal to the fourth surface S4. The fourth surface S4 is a bottomsurface of the light guide plate 200. Thus, the first downward incidentlight LA2 is reflected by the fourth surface S4 back into the lightguide plate 200, thereby forming first upward reflected light LA1′.

According to some embodiments, light emitted from the light source LSthat is incident to the light guide plate 200 includes a second upwardincident light LB1 that is incident onto the third surface S3 of thelight guide plate 200 at a second angle θB relative to the directionnormal to the third surface S3. The second angle θB is less than thecritical angle. Thus, the second upward incident light LB1 propagatesthrough the third surface S3 of the light guide plate 200 and isincident into the light conversion layer 300. In other words, the secondupward incident light LB1 propagates into the light conversion layer 300without an internal redirection from the light guide plate 200.

According to some embodiments, light emitted from the light source LSthat is incident to the light guide plate 200 also includes a seconddownward incident light LB2 that is incident onto the fourth surface S4of the light guide plate 200 at the second angle θB relative to thedirection normal to the fourth surface S4. Thereafter, the seconddownward incident light LB2 is reflected by the reflection sheet 400 orby the fourth surface S4 of the light guide plate 200. Such a secondupward reflected light LB2′ is incident onto the third surface S3 of thelight guide plate 200 at the second angle θB. Thus, the second upwardreflected light LB2′ propagates through the third surface S3 of thelight guide plate 200 and is incident into the light conversion layer300. In other words, the second downward incident light LB2′ propagatesinto the light conversion layer 300 without an internal redirection fromthe light guide plate 200.

According to some embodiments, unlike an afore-described embodiment,when light, such as the second upward incident light LB1 or the seconddownward incident light LB2, is incident into the light guide plate 200at the second angle θB less than the critical angle, it will be incidentinto the first portion 310 of the light conversion layer 300 withoutbeing reflected by the third surface S3 of the light guide plate 200. Inother words, an amount of light per unit area incident into the firstportion 310 is greater than an amount of light incident into the secondportion 320. Thus, an amount of light to be converted by the firstportion 310 is increased. This can reduce the brightness uniformity ofthe display device 1000. However, according to some embodiments of theinventive concept, since the first portion 310 of the light conversionlayer 300 is thinner than the second portion 320, an amount of lightconverted by the first portion 310 is less than an amount of lightconverted by the second portion 320, thus maintaining the brightnessuniformity of the display device 1000, even when an amount of light perunit area incident into the first portion 310 is greater than an amountof light per unit area incident into the second portion 320.

According to some embodiments of the inventive concept, incident lightpropagating from the light source LS toward the fourth surface S4 of thelight guide plate 200 include critical light that is incident onto thefourth surface S4 at the critical angle, and here, the critical light isreflected by the reflection sheet 400 back toward the third surface S3.The first region W1 may be defined as that portion of the third surfaceS3 to which the critical light reflected by the fourth surface isincident. In other words, a length of the first portion 310 in the firstdirection DR1 is determined by the critical angle of the critical light.In some embodiments, the length of the first portion 310 is proportionalto the critical angle of the critical light. In other embodiments, thelength of the first portion 310 is determined based on an angle at whichlight is emitted from the light source units LSU, a distance between thelight source unit LSU and the light guide plate 200, a thickness of thelight guide plate 200, and a refractive index of the light guide plate200.

As a result, according to some embodiments of the inventive concept, adisplay quality of the display device 1000 can be improved.

FIG. 6 is a sectional view of a backlight unit according to otherembodiments of the inventive concept, and FIG. 7 illustrates propagationpaths of light emitted from a light source according to otherembodiments of the inventive concept.

For concise description, a previously described element may beidentified by a similar or identical reference number without repeatinga description thereof. Other elements that are not separately describedmay have substantially the same technical features as those inpreviously described embodiments.

For convenience in illustration, those elements of a backlight unitother than a light guide plate and a light conversion layer are omittedfrom FIG. 6.

Referring to FIG. 6, in a light conversion layer according to otherembodiments of the inventive concept, a top surface of a first portion310-1 includes an inclined surface IS. The inclined surface IS extendsin the first direction DR1 and is inclined in a direction downward fromthe top surface of the second portion 320 toward the light source LS.

For example, in a present embodiment, the first portion 310-1 has athickness that gradually decreases with increasing distance from thesecond portion 320.

Referring to FIG. 7, according to some embodiments, light emitted by thelight source LS and incident to the light guide plate 200 includes thesecond upward incident light LB1 that is incident onto the third surfaceS3 of the light guide plate 200 at the second angle θB. The second angleθB is less than the critical angle. Thus, the second upward incidentlight LB1 propagates through the third surface S3 of the light guideplate 200 to be incident into the first portion 310-1. The second upwardincident light LB1 incident into the first portion 310-1 is reflected bythe inclined surface IS of the first portion 310-1, thereby forming asecond downward reflected light LB1′ propagating toward the light guideplate 200. The second downward reflected light LB1′ is incident onto thethird surface S3 at a third angle θC. Here, the third angle θC isgreater than the critical angle, and in this case, the second downwardreflected light LB1′ is re-incident into the light guide plate 200through the third surface S3.

According to some embodiments, light emitted from the light source LSand incident to the light guide plate 200 includes the second downwardincident light LB2 that is incident onto the fourth surface S4 of thelight guide plate 200 at the second angle θB. The second downwardincident light LB2 is reflected by the reflection sheet 400 or by thefourth surface S4 of the light guide plate 200 thereby forming a secondupward reflected light LB2′. The second upward reflected light LB2′ isincident onto the third surface S3 of the light guide plate 200 at thesecond angle θB. Thus, the second upward reflected light LB2′ propagatesthrough the third surface S3 of the light guide plate 200 and isincident into the first portion 310-1. The second upward reflected lightLB2′ incident into the first portion 310-1 is reflected by the inclinedsurface IS of the first portion 310-1, thereby forming a third downwardreflected light LB2″ that propagates toward the light guide plate 200.The third downward reflected light LB2″ has a fourth angle θD relativeto the third surface S3 and the fourth surface S4. The fourth angle θDis greater than the critical angle, and in this case, the third downwardreflected light LB2″ is re-incident into the light guide plate 200through the third surface S3. In some embodiments, the fourth angle θDis substantially equal to the third angle θC, but embodiments of theinventive concept are not limited thereto.

In a present embodiment, since the top, inclined surface IS of the firstportion 310-1 is inclined at an angle, even if light is incident intothe first portion 310-1 at an incident angle less than the criticalangle, the incident angle of the light relative to the normal to theinclined surface is of the first portion 310-1 may be increased. Thismakes it possible to prevent light from being concentrated in the firstregion W1 and can prevent structural differences between the first andsecond regions W1 and W2 from being recognized by a user.

FIG. 8 is a sectional view of a backlight unit according to otherembodiments of the inventive concept.

For concise description, a previously described element may beidentified by a similar or identical reference number without repeatinga description thereof. Other elements that are not separately describedmay have substantially the same technical features as those in thepreviously described embodiments.

Referring to FIG. 8, a backlight unit BLU-2 according to otherembodiments of the inventive concept further includes a low refractionlayer LR that is interposed between the light guide plate 200 and thelight conversion layers 310 and 320. The low refraction layer LR has athird refractive index. In some embodiments, the third refractive indexof the low refraction layer LR is less than those of the light guideplate 200 and the light conversion layer 310. For example, the thirdrefractive index ranges from about 1.15 to about 1.35.

FIG. 9 is a top plan view of a backlight unit BLU-3 according to otherembodiments of the inventive concept.

For concise description, a previously described element may beidentified by a similar or identical reference number without repeatinga description thereof. Other elements that are not separately describedmay have substantially the same technical features as those in thepreviously described embodiments.

Referring to FIG. 9, in a light conversion layer 300-3 according toother embodiments of the inventive concept, a number of quantum dots perunit volume in a first portion 310-3 is less than that in the secondportion 320. Furthermore, the number of quantum dots per unit volume inthe first portion 310-3 increases with decreasing distance from thesecond portion 320 or in the first direction DR1.

In a present embodiment, it is possible to effectively prevent theintensity of light from being locally increased at a specific region ofthe display device 1000, such as the first region W1.

FIG. 10 is a sectional view of a backlight unit BLU-4 according to otherembodiments of the inventive concept.

For concise description, a previously described element may beidentified by a similar or identical reference number without repeatinga description thereof. Other elements that are not separately describedmay have substantially the same technical features as those in thepreviously described embodiments.

Referring to FIG. 10, a light conversion layer according to otherembodiments of the inventive concept includes a first portion 310-4 thatincludes a plurality of patterns PT. Each of the plurality of patternsPT includes at least one of the first and second quantum dots QD1 andQD2.

In a present embodiment, the plurality of patterns PT are spaced apartfrom each other in the first direction DR1. A distance in the firstdirection DR1 between adjacent pairs of the patterns PT decreases withdecreasing distance from the second portion 320 or in the firstdirection DR1. In other words, the patterns PT have an increasingpattern density with decreasing distance from the second portion 320 orin the first direction DR1.

In a present embodiment, brightness uniformity of the display device1000 can be effectively improved.

FIG. 11 is a sectional view of a backlight unit according to otherembodiments of the inventive concept.

For concise description, a previously described element may beidentified by a similar or identical reference number without repeatinga description thereof. Other elements that are not separately describedmay have substantially the same technical features as those in thepreviously described embodiments.

Referring to FIG. 11, a backlight unit BLU-5 according to otherembodiments of the inventive concept further includes a scatteringmember SCT disposed on the light conversion layer 300. The scatteringmember SCT includes a plurality of scattering objects that areconfigured to scatter incident light.

In a present embodiment, the scattering member SCT is disposed on thesecond portion 320. The scattering member SCT does not overlap the firstportion 310, when viewed in a plan view.

According to some embodiments of the inventive concept, a displayquality of a display device can be improved. For example, according tosome embodiments of the inventive concept, brightness uniformity of thedisplay device can be improved.

While exemplary embodiments of the inventive concepts have beenparticularly shown and described, it will be understood by one ofordinary skill in the art that variations in form and detail may be madetherein without departing from the spirit and scope of the attachedclaims.

What is claimed is:
 1. A display device, comprising: a display panelconfigured to display an image; a light guide plate provided below thedisplay panel, the light guide plate including a side surface that is anincidence surface that is normal to a first direction; a light sourceadjacent to the incidence surface; and a light conversion layer disposedbetween the light guide plate and the display panel and configured tochange a wavelength of light incident thereto, wherein the lightconversion layer comprises a first portion and a second portion arrangedin the first direction, the first portion is closer to the incidencesurface in the first direction than the second portion, and the firstportion is thinner than the second portion.
 2. The display device ofclaim 1, wherein the second portion has a uniform thickness.
 3. Thedisplay device of claim 1, wherein the first portion has a uniformthickness.
 4. The display device of claim 1, wherein, when measured inthe first direction, a length of the first portion is less than about 5%of a length of the light guide plate.
 5. The display device of claim 1,wherein the first portion is connected to the second portion.
 6. Thedisplay device of claim 1, wherein a top surface of the first portioncomprises an inclined surface.
 7. The display device of claim 1, whereina thickness of the first portion increases in a direction from theincidence surface toward the second portion.
 8. The display device ofclaim 1, wherein the light conversion layer comprises a plurality ofquantum dots.
 9. The display device of claim 1, wherein the light sourceis configured to generate a first light, and the light conversion layercomprises: a first quantum dot converting the first light to a secondlight having a different wavelength range from that of the first light;and a second quantum dot converting the first light to a third lighthaving a different wavelength range from those of the first and secondlights.
 10. The display device of claim 9, wherein the first light is ablue light.
 11. The display device of claim 9, wherein a number ofquantum dots per unit volume in the first portion is less than that inthe second portion.
 12. The display device of claim 11, wherein thenumber of quantum dot per unit volume in the first portion increases ina direction from the incidence surface toward the second portion. 13.The display device of claim 1, wherein the first portion comprises aplurality of patterns that are spaced apart from each other in the firstdirection when viewed in a plan view, and a distance between adjacentpatterns of the plurality of patterns decreases in a direction from theincidence surface toward the second portion.
 14. The display device ofclaim 1, further comprising a low refraction layer interposed betweenthe light guide plate and the light conversion layer, wherein arefractive index of the low refraction layer is less than those of thelight guide plate and the light conversion layer.
 15. The display deviceof claim 1, further comprising a scattering member disposed on an uppersurface of the second portion that includes a plurality of scatteringobjects, wherein the scattering member does not overlap the firstportion, when viewed in a plan view.
 16. A backlight unit, comprising: alight guide plate that includes a side surface that is an incidencesurface; a light source provided adjacent to the incidence surface andconfigured to generate a first light; and a light conversion layerdisposed on the light guide plate, the light conversion layer comprisinga plurality of quantum dots that convert the first light into light thathas a different wavelength range from that of the first light, whereinthe light conversion layer includes a first region and a second regionarranged in a direction, the first region is closer to the incidencesurface than the second region, and a thickness of the light conversionlayer in the first region is less than that in the second region. 17.The backlight unit of claim 16, wherein the plurality of quantum dotscomprise: a plurality of first quantum dots that convert the first lightto a second light having a different wavelength range from that of thefirst light; and a plurality of second quantum dots that convert thefirst light to a third light having a different wavelength range fromthose of the first and second lights.
 18. The backlight unit of claim16, wherein, an area of a top surface of the first region is less thanabout one-twentieth of a total area of a top surface of the light guideplate.
 19. The backlight unit of claim 18, wherein the light conversionlayer in the second region has a uniform thickness.
 20. The backlightunit of claim 18, wherein a thickness of the light conversion layer inthe first region increases in a direction from the incidence surfacetoward the second region.